1. Field of the Invention
A method used in a wireless communication system and related communication device are provided, and more particularly to, a method of formatting dynamic scheduling information (DSI) for a mobile device in a wireless communication system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
A multimedia broadcast multicast service (MBMS) has been introduced in LTE specification. The MBMS gives the opportunity to broadcast TV, film, information such as free overnight transmission of newspaper in digital form and other media in these networks. The broadcast capability enables to reach unlimited number of users with constant network load. Further, it also enables the possibility to broadcast information simultaneously to many cellular subscribers. In a MBMS Single frequency network (MBSFN) area, a group of cells are coordinated for an MBSFN transmission and transmit the same content for the UEs.
In order to support the UE to receive MBMS data, the eNB provides the UE with information about MBSFN subframes used for MBMS control channel (MCCH), Multicast traffic channel (MTCH) and dynamic scheduling information (DSI). The MTCH is a point-to-multipoint downlink channel for transmitting data traffic from the network to the UE. The MCCH is a point-to-multipoint downlink channel used for transmitting MBMS control information from the network to the UE, for one or several MTCHs. The eNB performs multimedia access control (MAC)-level multiplexing for different MTCHs to be transmitted on a multicast channel (MCH). The MCH is used to transport user data and the control message. Both of the MCCH and the MTCH are mapped to the MCH. Multiple MBMS services can be transmitted using a single MTCH, provided that they use the same MBSFN area. One MCH can only contain data belonging to one MBSFN area; multiplexing between different MBSFN areas is not supported since MBSFN areas composed of different sets of cells would have different composite channel responses and need different channel estimations. It is most likely for several MBMS services to be transmitted on one MBSFN subframe, a logical channel identifier (LCID) included in a MAC header is used for the UE to identify the MBMS services of interest.
However, the MCHs transmitted over different MBSFN areas can be multiplexed in different MBSFN subframes. Within the MBSFN subframes, the transmission of a specific MCH occupies a pattern of MBSFN subframes, not necessarily adjacent in time, called the MCH Subframe Allocation Pattern (MSAP). The MSAP for every MCH carrying MTCH is signalled on MCCH. The MSAP occasion comprises the set of MBSFN subframes defined by the MSAP during a certain period. Within each MSAP occasion, additional signaling indicates the order in which the MTCHs are multiplexed.
The transmission order of MTCHs is signalled (implicitly or explicitly) in the MCCH. The dynamic scheduling information can be provided per MCH to indicate which subframes are used by each MTCH in the MSAP occasion.
It is possible that some of ongoing MBMS services are not scheduled or no data for transmission in current scheduling period. Therefore, DSI is necessary to indicate the scheduled MTCH (s) so that UE can correctly receive the interested services. Several candidate solutions are described as follows:
Alternative 1(A1): a bitmap+a list of start/stop tags for all scheduled MTCHs
Alternative 2 (A2): a list of {LCID, start/stop tags} for all scheduled MTCHs
Alternative 3(A3): a list of start/stop tags for all MTCHs, and using a special start/stop value to indicate unscheduled MTCHs
Alternative 4 (A4): a toolbox” approach where (1 or 2-bit) flag is used to indicate which of above alternatives is used
Where, the bitmap indicates scheduling status of all services listed in MCCH. In the bitmap, one bit associates with one service in MCCH. For example, “1” means scheduled service, and “0” means non-scheduled service. The real options are A1, A2 and A3. For A1 and A2, the relation between required bits and scheduled MTCHs is fixed. Since there is no bitmap or LCID list for A3, it is not clear how many bits are required.